N. F. Kharchenko

Weak ferromagnetism in the antiferromagnetic magnetoelectric crystal LiCoPO4

A study of the magnetization of the antiferromagnetic magnetoelectric crystal LiCoPO4 as a function of temperature and the strength of a magnetic field oriented along the antiferromagnetic vector reveals features due to the presence of a weak ferromagnetic moment. The value of the magnetic moment along the b axis at 15 K is approximately 0.12 G. The existence of a ferromagnetic moment can account for the anomalous behavior of the magnetoelectric effect observed previously in this crystal.

Magnetic field induced spin reorientation in the strongly anisotropic antiferromagnetic crystal LiCoPO4

It has been found experimentally that in the strongly anisotropic orthorhombic antiferromagnetic crystal LiCoPO4 (TN=21.7K) the destruction of antiferromagnetic order by a magnetic field directed along the antiferromagnetism axis H∥b occurs in steps by means of three phase transitions: two first-order transitions in the fields H1=118kOe, H2=224Oe and one second-order phase transition in the field H3=283kOe (T=1.7K). A section of magnetic fields (H2, H3) where the magnetization of the crystal varies almost linearly with the field was found. Possible magnetic structures formed in a magnetic field are discussed. The values of the exchange parameters are estimated.

Nonmonotonic temperature dependence of the spontaneous magnetization of the antiferromagnetic crystal LiCoPO4

The temperature dependence of the magnitude of the weak ferromagnetic moment is measured in the many-sublattice antiferromagnetic magnetoelectric crystal LiCoPO4. The dependence is found to be nonmonotonic—as the temperature is decreased below the Neel temperature TN, the ferromagnetic moment initially increases and then decreases markedly. It reaches its highest value, close to 0.12 G, at a temperature of around 10.5 K, which is roughly TN/2. The possible mechanisms for the appearance of weak ferromagnetism in LiCoPO4 and the causes of the nonmonotonic temperature dependence of the spontaneous magnetic moment are discussed. Among the possible mechanisms, there is a preference for one in which the weak ferromagnetism is due to a nonuniform antiferromagnetic structure which is proposed for this crystal.

Magnetic field induced increase of the longitudinal Kerr effect in multilayer Co∕Cu(111) films

A many-fold increase of the longitudinal Kerr effect in a magnetic field has been found in multilayer Co∕Cu(111) films for definite thicknesses of the copper layers, which give extrema of the exchange coupling between the cobalt layers. It is conjectured that this phenomenon is due to the presence of a large contribution of the Co/Cu interfaces to the magneto-optic effect and is due to the paramagnetism of the conduction electrons in the interface layers, increased by hybridization of the electronic sp and d bands of copper and cobalt. It is conjectured that the periodic increase of the magneto-optic susceptibility is due to the sensitivity of the hybridization to the quantization of the transverse motion of the electrons in the copper layers.

Odd magnetic dichroism of linearly polarized light in the antiferromagnet MnF2

The two-sublattice tetragonal antiferromagnetic crystal manganese fluoride is found to exhibit dichroism induced by a magnetic field H∥C4∥Z for linearly polarized light propagating along the tetragonal axis of the crystal also. The observed effect is odd with respect to the sign of the z projection of the field and the operation of reversing the directions of the sublattice magnetic moments of the antiferromagnet. The effect can be used for optical visualization of 180-degree (time-reversed) antiferromagnetic domains in MnF2.

Quadratic in field contribution to the magnetization of antiferromagnetic CoF2

Abstract The quadratic in magnetic field contribution to the magnetization has been observed in the two-sublattice tetragonal antiferromagnetic CoF 2 by SQUID measurements. The measured value of the C xyz component of the second-order nonlinear susceptibility tensor is equal to 5.75×10 −9 emu cm −3 Oe −2 or 1.21×10 −7 emu mol −1 Oe −2 at 6 K.

Reduction of superparamagnetic clusters in the [Co/Cu(111)]n nanofilms, induced by the quantum size effect

It is known that the quantum size effects are important for the formation of morphological properties of metal films. The regularities in the behavior of the superparamagnetic magnetoresistive effect in multilayer nanofilms Co/Cu(111) in a magnetic field, found in the work, indicate the influence of the electron size effect on the formation of clusters in these films. The results of measurements of the high-field magnetoresistive effect are reported for multilayer films [Co/Cu(111)]20 with a constant thickness of cobalt layers and the thickness of copper layer varying from film to film. It is found that an effective size of superparamagnetic formations is reduced in the films with thickness of the copper layers corresponding to the maxima of the antiferromagnetic exchange coupling between cobalt layers. It is suggested that the observed “grinding” of superparamagnetic particles is caused by oscillating changes in the electron density in the interface layer Co/Cu, induced by electron quantum size effect in...

The effect of FR enhancement in reactive ion beam sputtered Bi, Gd, Al-substituted iron-garnets: Bi 2 O 3 nanocomposite films

The effect of considerable Faraday rotation (FR) and figure of merit (Q) enhancement in Bi, Gd, Al-substituted iron garnets: Bi<inf>2</inf>O<inf>3</inf> nano-composite films produced by separate reactive ion beam sputtered Bi:YIG and Bi<inf>2</inf>O<inf>3</inf> films was found. It reached threefold enhancement of the FR and twofold of the Q one on GGG substrates.

Schottky anomaly of linear birefringence of light in the antiferromagnetic crystal LiCoPO4

Anomalous behavior of the birefringence of linearly polarized light has been observed in the antiferromagnetic magnetoelectric crystal LiCoPO4 at temperatures approaching the Neel temperature. Arguments are present in support of the assumption that the observed nonmonotonic change of the birefringence of light is due to the interplay of two anomalies—a magnetic anomaly, associated with the intensification of the contribution of correlated spin fluctuations, and the Schottky anomaly, due to the changing occupations of the ground and lowest excited electronic states of Co2+ ions. The estimate of the energy splitting from the excited state (45–55K) agrees satisfactorily with the position of the weakly dispersing branch in the energy spectrum of this crystal, observed in an investigation of the inelastic scattering of neutrons, as well as with the energies of the low-energy bands in the Raman scattering spectrum.Anomalous behavior of the birefringence of linearly polarized light has been observed in the antiferromagnetic magnetoelectric crystal LiCoPO4 at temperatures approaching the Neel temperature. Arguments are present in support of the assumption that the observed nonmonotonic change of the birefringence of light is due to the interplay of two anomalies—a magnetic anomaly, associated with the intensification of the contribution of correlated spin fluctuations, and the Schottky anomaly, due to the changing occupations of the ground and lowest excited electronic states of Co2+ ions. The estimate of the energy splitting from the excited state (45–55K) agrees satisfactorily with the position of the weakly dispersing branch in the energy spectrum of this crystal, observed in an investigation of the inelastic scattering of neutrons, as well as with the energies of the low-energy bands in the Raman scattering spectrum.

Magnetic linear dichroism of an antiferromagnetic MnF2 crystal: Oddness in two different antiferromagnetic states

Dichroism of linearly polarized light propagating along the tetragonal C4 axis, induced by a longitudinal magnetic field, has been revealed in a tetragonal antiferromagnetic manganese fluoride crystal in the region of optical transitions. The magnetic linear dichroism observed is proportional to the magnetic field strength and odd with respect to the field sign. The value of the effect is sufficient for optical observation of antiferromagnetic domains in MnF2 crystals.